The Huasteca Potosina occupies a geological fault line where the Sierra Madre Oriental meets the coastal plain, creating a karst landscape of over two hundred rivers, cenotes, and waterfalls within a fifty-kilometer radius of Ciudad Valles. The region remained largely inaccessible until the mid-twentieth century, when Pemex engineers surveying oil fields discovered river systems that had carved through Cretaceous limestone for sixty million years. Today the confluence of three hydrological basins — the Valles, Tampaón, and Moctezuma — sustains ecosystems that range from cloud forest at twelve hundred meters to tropical lowland corridors where migratory birds from the Great Plains winter alongside resident macaw populations. Ciudad Valles serves as the logistical gateway, a market town of sixty thousand that sits at the transition zone between temperate highland and humid subtropics. The town's position fifteen kilometers from the first major cascade, Tamul, made it a natural departure point when ecotourism infrastructure began developing in the nineteen-nineties. Tours Huasteca Potosina saliendo de Ciudad Valles now depart daily for sites that were accessible only by mule or canoe a generation ago. The Tamul waterfall drops one hundred five meters into a canyon where the Gallinas River joins the Tampaón, creating a natural amphitheater visible only from the water or from a narrow canyon rim trail. The surrealist sculptor Edward James purchased a thirty-seven-hectare tract near Xilitla in nineteen forty-seven and spent three decades constructing Las Pozas, a concrete garden of spiral staircases, arched colonnades, and unroofed pavilions integrated into the existing waterfall network. James worked without blueprints, directing a rotating crew of local masons to build structures that frame rather than replace the jungle canopy. The site includes thirty-six concrete sculptures and nine natural pools fed by the Río Choy, which maintains a year-round temperature of twenty-two degrees Celsius. Tours Huasteca Potosina saliendo de Ciudad Valles that include Las Pozas typically pair the garden with visits to either the Sótano de Huahuas, a three-hundred-meter vertical shaft where military macaws and green parakeets roost, or the Puente de Dios, a natural limestone bridge spanning the Choy where the river has eroded a series of turquoise pools and submerged caves. The geology here is active: travertine deposits continue to form at a rate of two millimeters per year, and the river's alkaline chemistry supports endemic freshwater sponges found nowhere else in the Sierra Madre.